Hi @johsflesj​,

The TINSurface output of the TINGenerator is written to AutoCAD as a mesh, which does not appear to be suitable for conversion to a Civil 3D surface.

Instead, connect the Triangles output of the TINGenerator to a FaceReplacer to create faces from the triangles, then write the faces to AutoCAD.

In Civil 3D, create a new surface in the Prospector tab of the TOOLSPACE side menu. Right-click on the Definition - Drawing Objects of the new Surface, then choose Add. In the dialog that opens, set Object type to 3D Faces and check the 'Maintain edges from object' box. Select all the faces in the DWG, then accept to add them to the Surface.

Thanks @daveatsafe​.

I would like to avoid manually processes in AutoCAD, if possible. My intention is to automate a workflow where writing TINs to DWG is crucial. Is there any way I can automate this process?

Perhaps an AutoCAD script (SCR)? They can be run from the command line without human intervention, and you can include the save and quit commands in the script to have them exit Civil3D automatically when done. You would need to find the commands for the TIN creation and surface conversion, though, since SCRs can't pick from the menu.